Phenylalanine, tyrosine, and tryptophan are amino acids with an aromatic (benzene) ring that are relatively nonpolar aand participate in hydrophobic interactions.

At a pH of 12, the amino group for all of the amino acids would be deprotonated, resulting in at least a charge from the acid group. Another negative charge comes from the carboxyl group on the backbone. Tyrosine is amphipathic, and the pKa of its sidechain is 10.8, meaning it is a deprotonated at a pH of 12. This gives it a charge at a pH of 12. Tryptophan has no side-chain pKa so 3 equivalence points would not be seen. Threonine would also not have 3 equivalence points. Glutamic acid doesn't have amphipathic properties. Histidine is amphipathic, but it is a basic amino acid.

Cysteine and methionine are the only two amino acids that are incorporated into proteins which contain sulfur. However, only cysteine can form disulfide bonds due to its free SH group. Methionine does not have a free SH group and thus cannot form these bonds.

Selenocysteine is a rare amino acid residue that is incorporated during protein synthesis (instead of during post-translational modifications as is the case with other rare residues). It is made from serine, but it looks like cysteine with a selenium atom in place of the sulfur atom. It is only found in a few known proteins including glutathione peroxidases. Selenocysteine has a lower pKa and lower reduction potential than cysteine.

Only aspartate and threonine have side chains capable of hydrogen bonding interactions. Aspartate has a terminal carboxylate which can act as a hydrogen bond acceptor and as a hydrogen bond donor when protonated. Threonine has a terminal hydroxyl group which can also act as a hydrogen bond donor. Alanine has an entirely aliphatic side chain which is unable to participate in hydrogen bonding, and methionine has a sulfhydryl group, that cannot participate in hydrogen bonding.

Amino acid polymerization (translation) involves condensation, or the production of free water. For each peptide bond that is formed, one molecule of water is also formed. Myoglobin contains 154 amino acids, thus contains 153 peptide bonds and 153 molecules of water produced per protein synthesized.

The guanidino group of arginine is protonated in solutions with pH at or below the pKa of 12.5. It is a positively charged basic side chain that becomes neutral at a pH 12.5 or greater.

Serine and tyrosine both have uncharged polar side chains with one hydroxyl group, but only tyrosine has a pKa value for its side chain of 10.5. This indicates that tyrosine will lose its proton above pH 10.5 and is therefore neutral at pH 7.0.

A transmembrane protein consists of two hydrophilic regions (that are found on the ends facing the cytoplasmic and extracellular sides) and one hydrophobic region (inserted into the hydrophobic interior of the phospholipid bilayer). The question states that the region is saturated with valine amino acid residues. Recall that valine is a hydrophobic amino acid; therefore, the region containing lots of valine residues must be the hydrophobic region of the transmembrane protein.

Since this is an ion-exchange chromatography method, we expect that the protein found in the column has the opposite charge of the beads. Since the beads were negatively charged, we expect the amino acid to be positively charged. Lysine has a basic side chain that can easily pick up a hydrogen from solution and become positively charged.

We're told in the question that this amino acid has a pI = 10.4. Therefore, we expect this to be a basic amino acid. This means that one carboxyl group, one amino group, and one basic R-group will be present.

At the start of the titration, the solution starts out acidic at a very low pH. At a pH of 2, since so many protons are in solution at this pH, all of the important functional groups under consideration will be protonated. Thus, the amino acid will have a positive charge on each of its basic functional groups, and a neutral charge on its carboxyl group, giving the amino acid a net charge of +2.

Once the pH has climbed to a value of 8, we would expect that only the carboxyl group will be deprotonated. As a result, the carboxyl group will have a negative charge, while each of the other two basic functional groups will still retain their positive charge. Thus, the amino acid at this pH will have a net charge of +1.

And finally, once the pH climbs all the way up to a value of 12, we can expect the two basic functional groups to be deprotonated. Consequently, each of the basic functional groups will be neutral, while the carboxyl group will still be negative. Thus, the overall charge of the amino acid will be negative at this pH.

So overall, the amino acid will be positive, then positive, followed by negative.